siRNAs and RNA interference
RNA interference (RNAi) is a phenomenon involving double-stranded (ds) RNA-dependent gene specific posttranscriptional silencing. Originally, attempts to study this phenomenon and to manipulate mammalian cells experimentally were frustrated by an active, non-specific antiviral defence mechanism which was activated in response to long dsRNA molecules; see Gil et al. 2000, Apoptosis, 5:107-114. Later it was discovered that synthetic duplexes of 21 nucleotide RNAs could mediate gene specific RNAi in mammalian cells, without the stimulation of the generic antiviral defence mechanisms (see Elbashir et al. Nature 2001, 411:494-498 and Caplen et al. Proc Natl Acad Sci 2001, 98:9742-9747). As a result, small interfering RNAs (siRNAs), which are short double-stranded RNAs, have become powerful tools in attempting to understand gene function.
Thus, RNA interference (RNAi) refers to the process of sequence-specific post-transcriptional gene silencing in mammals mediated by small interfering RNAs (siRNAs) (Fire et al, 1998, Nature 391, 806) or microRNAs (miRNAs) (Ambros V. Nature 431:7006, 350-355 (2004); and Bartel D P. Cell. 2004 Jan. 23; 116 (2): 281-97 MicroRNAs: genomics, biogenesis, mechanism, and function). The corresponding process in plants is commonly referred to as specific post-transcriptional gene silencing or RNA silencing and is also referred to as quelling in fungi. An siRNA is a double-stranded RNA molecule which down-regulates or silences (prevents) the expression of a gene/mRNA of its endogenous (cellular) counterpart. RNA interference is based on the ability of dsRNA species to enter a specific protein complex, where it is then targeted to the complementary cellular RNA and specifically degrades it. Thus, the RNA interference response features an endonuclease complex containing an siRNA, commonly referred to as an RNA-induced silencing complex (RISC), which mediates cleavage of single-stranded RNA having a sequence complementary to the antisense strand of the siRNA duplex. Cleavage of the target RNA may take place in the middle of the region complementary to the antisense strand of the siRNA duplex (Elbashir et al 2001, Genes Dev., 15, 188). In more detail, longer dsRNAs are digested into short (17-29 bp) dsRNA fragments (also referred to as short inhibitory RNAs—“siRNAs”) by type III RNAses (DICER, DROSHA, etc., Bernstein et al., Nature, 2001, v. 409, p. 363-6; Lee et al., Nature, 2003, 425, p. 415-9). The RISC protein complex recognizes these fragments and complementary mRNA. The whole process is culminated by endonuclease cleavage of target mRNA (McManus&Sharp, Nature Rev Genet, 2002, v. 3, p. 737-47; Paddison &Hannon, Curr Opin Mol Ther. 2003 June; 5(3): 217-24). For information on these terms and proposed mechanisms, see Bernstein E., Denli A M. Hannon G J: 2001 The rest is silence. RNA. I; 7(11): 1509-21; Nishikura K.: 2001 A short primer on RNAi: RNA-directed RNA polymerase acts as a key catalyst. Cell. I 16; 107(4): 415-8 and PCT publication WO 01/36646 (Glover et al).
The selection and synthesis of siRNA corresponding to known genes has been widely reported; see for example Chalk A M, Wahlestedt C, Sonnhammer E L. 2004 Improved and automated prediction of effective siRNA Biochem. Biophys. Res. Commun. June 18; 319(1): 264-74; Sioud M, Leirdal M., 2004, Potential design rules and enzymatic synthesis of siRNAs, Methods Mol Biol.; 252:457-69; Levenkova N, Gu Q, Rux J J. 2004, Gene specific siRNA selector Bioinformatics. I 12; 20(3): 430-2. and Ui-Tei K, Naito Y, Takahashi F, Haraguchi T, Ohki-Hamazaki H, Juni A, Ueda R, Saigo K., Guidelines for the selection of highly effective siRNA sequences for mammalian and chick RNA interference Nucleic Acids Res. 2004 I 9; 32(3):936-48.Se also Liu Y, Braasch D A, Nulf C J, Corey D R. Efficient and isoform-selective inhibition of cellular gene expression by peptide nucleic acids, Biochemistry, 2004 I 24; 43(7):1921-7. See also PCT publications WO 2004/015107 (Atugen) and WO 02/44321 (Tuschl et al), and also Chiu Y L, Rana T M. siRNA function in RNAi: a chemical modification analysis, RNA 2003 September; 9(9):1034-48 and I U.S. Pat. Nos. 5,898,031 and 6,107,094 (Crooke) for production of modified/more stable siRNAs.
Several groups have described the development of DNA-based vectors capable of generating siRNA within cells. The method generally involves transcription of short hairpin RNAs that are efficiently processed to form siRNAs within cells. Paddison et al. PNAS 2002, 99:1443-1448; Paddison et al. Genes & Dev 2002, 16:948-958; Sui et al. PNAS 2002, 8:5515-5520; and Brummelkamp et al. Science 2002, 296:550-553. These reports describe methods to generate siRNAs capable of specifically targeting numerous endogenously and exogenously expressed genes.
Several studies have revealed that siRNA therapeutics are effective in vivo in both mammals and in humans. Bitko et al., have shown that specific siRNA molecules directed against the respiratory syncytial virus (RSV) nucleocapsid N gene are effective in treating mice when administered intranasally (Bitko et al., Nat. Med. 2005, 11(1):50-55). For reviews of therapeutic applications of siRNAs see for example, Barik (Mol. Med 2005, 83: 764-773); Chakraborty (Current Drug Targets 2007 8(3):469-82) and Dykxhoorn, et al (Gene Therapy 2006, 13, 541-552). Furthermore, a phase I clinical study with short siRNA molecule that targets the VEGFR1 receptor for the treatment of Age-Related Macular Degeneration (AMD) has been conducted in human patients. In studies such siRNA administered by intravitreal (intraocular) injection was found effective and safe in 14 patients tested (Kaiser, Am J Ophthalmol. 2006 142(4):660-8).
The Nrf2 Gene and Polypeptide (gi|166295208|ref|NM—006164.3| Homo sapiens Nuclear Factor (Erythroid-Derived 2)-Like 2 (NFE2L2):
Nuclear factor erythroid-2 related factor 2 (Nrf2), a cap-and-collar basic leucine zipper transcription factor, positively regulates a transcriptional program that maintains cellular redox homeostasis and protects cells from oxidative insult, including insult from chemotherapeutic agents (Rangasamy T, et al. J Clin Invest 114, 1248 (2004)). Nrf2 activates transcription of its target genes through binding specifically to the antioxidant-response element (ARE) found in those gene promoters. The Nrf2-regulated transcriptional program includes a broad spectrum of genes, including antioxidants such as heme oxygenase-1, superoxide dismutase, glutathione reductase (GSR), glutathione peroxidase, thioredoxin, thioredoxin reductase, peroxiredoxins (PRDX).
Lung Cancer:
Lung cancer is a cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on the morphology of the cells under a microscope. It is the most lethal of all cancers worldwide, responsible for up to 3 million deaths annually. In non-small cell lung cancer (NSCLC), results of standard treatment are poor except for the most localized cancers. Surgery is the most potentially curative therapeutic option for this disease; radiation therapy can produce a cure in a small number of patients and can provide palliation in most patients. Adjuvant chemotherapy may provide an additional benefit to patients with resected NSCLC. In advanced-stage disease, chemotherapy offers modest improvements in median survival, though overall survival is poor. Chemotherapy has produced short-term improvement in disease-related symptoms.
WO 2006/128041 discloses specific siRNA molecules for Nrf2 and its use for treating any cancer, preferably lung and kidney cancers. US20020164576 discloses a method of inhibiting tumor growth (preferably a lymphoma cancer) using antisense molecules directed to Nrf2 or specific antibodies. US20070042418 discloses the use of siRNA molecules for Nrf2 for treating cancer.
Despite the evident progress, there remains a continued need for improved molecules in particular improved siRNA compounds able to treat cancerous diseases, particularly lung cancers.